I had understood your request.
I try to explain a bit differently.
In the page you are referring to, there are several small sub-chapters and in the header I set only the parent chapter.
And when the parent chapter is short, there will be no detail in the header.
There are many cases like those you report.
For the moment I will leave it as it is.
Thank you Andrew, sorry I did not see this.
We need quite some often, at least me, other eyes to see the evidence ,
Of course, amended for the next edition.